OK: So What's a Gravel Bike Mullet Build?

Business in the front, party in the back.

OK, the name is more than a little cringeworthy.  But given the saying about the haircut for which it's named, it isn't hard to understand why mullet might be an appropriate description for road/mountain hybrid drivetrains.  Taking advantage of the cross-compatibility within SRAM's AXS wireless drivetrains, Mullet builds use road drop bar brake/shift levers to control mountain rear derailleurs, cassettes, and chains.  The best of both worlds?  Well, they might just be.

It's not mystery that at Lindarets we spend a lot of time thinking and talking about bicycle -and specifically gravel bike- drivetrains and gearing.  There are countless combinations of drivetrain components, gear ratios, perspectives, and rider preferences, which can make building the 'right' bike awfully daunting.  

J.Guillem Atalaya Titanium Gravel Bike with AXS Mullet Drivetrain

Much of the resistance to single-ring chainrings comes from a couple of places.  First, the lack of range- the breadth of gear choices between the highest and lowest options.  The widest-range Shimano Ultegra road group has a 428% range- in other words, the highest gear is 4.28 times the lowest.  The gravel-oriented GRX 8xx groups offer 460%. The first proper gravel 1x group (SRAM's Force1) has a near-Ultegra 420% range thanks to its wide-range cassette.

Gravel Bike Gear Ratios and Speed

There are visual, weight, noise, and chain security advantages to single-ring drivetrains.  The big tradeoff comes in the form of step size.  Tooth count doesn't really tell the story: shifting from an 11t to a 13t cog makes a much bigger difference in terms of cadence than a 15-17 or 25-27 shift.  Road cassette steps tend to top out around 15% and average roughly 10% between adjacent cogs.  Wide-range gravel and mountain cassettes top out at about 17% and average 13-14% between cogs.  

Does it make a difference?  It depends on the rider.  Most of us were taught to keep our cadence around 90rpm.  Upshifting from 90 would put a rider at 81rpm on a GRX/Ultegra cassette, on a wide range cassette that same upshift would put the same rider at 79rpm.  It may feel like a big difference in the moment, but on mixed terrain it's less noticeable than when road riding in a pack.

So why are Mullet Bikes exciting?  Adding a twelfth cog makes a double-beating 500% possible, without resorting to uncomfortably large steps.  The 14% average step shown above is a little misleading- gears 2-12 are the same as 1-11 on a 13% average Force1 10-42, with an extra-low 50t first cog.  

SRAM Force & Red AXS Drivetrain Ratios with Mullet XX1 X01 Eagle Option

Compared to the more road-focused Force AXS 2x12 drivetrains, a Mullet build offers more range, a wider mountain-proven Eagle 12-speed chain, and a more secure mountain bike clutched derailleur.  And, in what may come as a surprise, the steps between cogs are more consistent, with nice smooth curve from highest gear to lowest.  

Despite the truly massive cassette, removing redundant parts saves roughly 1/2lb over a similar 2x build.  Right or wrong, we can't help ourselves when it comes to shaving weight- and we've seen far, far, far worse ways to shave 1/2lb from a bicycle.

J.Guillem Atalaya Titanium Gravel Bike with AXS Mullet Drivetrain

Ergonomically, SRAM Red and Force AXS drivetrains are hard to fault- they can be programmed to work any number of ways, but typically leave our shop with the right paddle shifting down the cassette, the left shifting back up.  The hydraulic disc brakes are powerful and easy to modulate and the lack of shift wires further emphasize the Atalaya's already clean lines.

Are mullet builds the right choice for everyone?  Maybe not.  And if the majority of your rides are on paved roads probably not- doubles and tighter ratios still rule on group rides and gradual climbs.  Which is why we offer both.  But for those who spend the bulk of their time on rough roads or climbing and descending steeper terrain the advantages are real- and the drawbacks are probably smaller than a lot of riders might think.

J.Guillem Atalaya Titanium Gravel Bike with SRAM AXS Force XX1 Mullet Group and Spinergy GX Wheels